<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button id="startBtn">开始计时</button>
    <button id="stopBtn">停止计时</button>
    <div id="app">
        hello
    </div>
</body>
<script src="../js/demo6.js"></script>

</html>